1. Field of the Invention
The invention relates to an improved process for preparing 3-acyloxy-2-methylbenzoic acids by heating substituted naphthalenes in the presence of alkali metal hydroxides and subsequently acylating.
2. Brief Description of the Prior Art
3-Acyloxy-2-methylbenzoic acids, for example 3-acetoxy-2-methylbenzoic acid, are valuable intermediates in the preparation of pharmaceuticals, for example HIV protease inhibitors (see, for example, U.S. Pat. No. 5,484,926) and agrochemicals.
EP-A 891 964 discloses a process for preparing such compounds which starts from 3-amino-1,5-naphthalenedisulphonic acid or its alkali metal salts and proceeds via the reaction with alkali metal hydroxide, removal of insolubles and reaction with acetic anhydride.
A disadvantage of this process is the use of the expensive 3-amino-1,5-naphthalenedisulphonic acid or its salts and also the unsatisfactory overall yield of 60%.
There is therefore a need to develop an efficient process which enables the preparation of 3-acyloxy-2-methylbenzoic acids in an advantageous manner.